The gasification process involves turning coal or other carbon-containing materials into synthesis gas. Because coal costs less than natural gas and oil, there is a large economic incentive to develop gasification technology. An issue with existing gasification technologies is that they generally have high capital costs and/or relatively low availability. Availability refers to the amount of time the equipment is on-line and making products. One cause of low availability is complex or short-lived gasifier liner designs. Examples of liners currently being used in gasifiers are refractory liners, membrane liners, and regeneratively cooled liners. Refractory liners require annual replacement of the refractory, with an availability of approximately 90%. While membrane liners have a longer life than refractory liners, the complexity of the liner can increase the cost of the gasifier up to 2 to 3 times.
Regeneratively cooled liners are also used in the gasification process and generally present a lower cost, longer life alternative to refractory liners and membrane liners. These benefits are a result of freezing a layer of slag on the wall of the regeneratively cooled liner. Regeneratively cooled liners can significantly reduce the cost of electricity, hydrogen, and synthesis gas produced by gasification plants when compared to gasification plants using refractory liners and membrane liners. An example of a regeneratively cooled liner is disclosed in U.S. Pat. No. 6,920,836 (Sprouse), which is herein incorporated by reference.
While regeneratively cooled liners provide significant benefits in gasification technology when compared to refractory liners and membrane liners, one of the technical challenges of using regeneratively cooled liners is managing the thermal growth of the liner. The liner, which may be formed of ceramic, is usually attached to a metal backing structure of the gasifier. Thus, as the temperature inside the gasifier increases, the rates of thermal expansion of the ceramic liner and the metal backing structure are mismatched.
Another challenge with regard to regeneratively cooled liners is the specific implementation of the metal/ceramic joining required to establish a closed-loop (regenerative) cooling circuit. In addition, there is a risk that a small crack in the liner could alter the performance and efficiency of the gasifier, eliminating the ability to co-generate power.
Thus, a need exists for a gasifier liner that offers the advantages of a ceramic lining while addressing the challenges of ceramic/metal joining and ceramic/metal thermal growth mismatch.